Ballistic-resistant article

ABSTRACT

Articles such as vests, helmets and structural elements containing a network of ultrahigh molecular weight, high strength, high modulus polyethylene or polypropylene fibers. The fibers, and especially polyethylene fibers of 15, 20, 25, 30 or more g/denier tenacity, and 300, 500, 1000, 1500 or more g/denier tensile modulus impart exceptional ballistic resistance to the articles in spite of the melting points, e.g. 145 DEG -151 DEG  C. for the polyethylene fibers and 168 DEG -171 DEG  C. for the polypropylene fibers, which are high for these polymers, but substantially lower than the 200 DEG  C. or more melting point previously thought necessary for good ballistic resistance.

This application is related to four copending, commonly assignedapplications filed herewith, each of which is incorporated herein byreference to the extent not inconsistent herewith:

Kavesh et al., "Producing High Tenacity, High Modulus CrystallineThermoplastic Article Such As Fiber or Film," Ser. No. 359,020, fledMar. 19, 1982, a continuation-in-part of Ser. No. 259,266, filed Apr.30, 1981.

Kavesh et al., "High Tenacity, High Modulus Polyethylene andPolypropylene Fibers, And Gel Fiber Useful In The Production Thereof,"Ser. No. 359,019, filed Mar. 19, 1982, a continuation-in-part of Ser.No. 259,266, filed Apr. 30, 1981;

Harpell et al., "Improved Ballistic-Resistant Article," Ser. No.359,975, filed Mar. 19, 1982, now U.S. Pat. No. 4,403,012.

Harpell et al., "Coated Extended Chain Polyolefin Fiber," Ser. No.359,976, filed Mar. 19, 1982.

BACKGROUND OF THE INVENTION

Ballistic articles such as bulletproof vests, helmets, structuralmembers of helicopters and other military equipment, vehicle panels,briefcases, raincoats and umbrellas containing high strength fibers areknown. Fibers conventionally used include aramids such aspoly(phenylenediamine terephthalamide), graphite fibers and the like.For many applications, such as vests or parts or vests, the fibers areused in a woven or knitted fabric. For many of the other applications,the fiber is encapsulated or embedded in a composite material.

A number of properties are generally considered to be necessary for thehigh strength fiber to be useful as a ballistic resistant material. Fourof these factors listed by John V. E. Hansen and Roy C. Laible, in"Fiber Frontiers" ACS Conference, (June 10-12, 1974), entitled "FlexibleBody Armor Materials" are higher modulus, higher melting point, higherstrength and/or work-to-rupture values and higher resistance to cuttingor shearing. With regard to melting point, it is indicated as desirableto retard, delay or inhibit the melting seen with nylon and polyester.In a book entitled "Ballistic Materials and Penetration Mechanics", byRoy C. Laible (1980), it is indicated that no successful treatment hasbeen developed to bring the ballistic resistance of polypropylene up tothe levels predicted from the yearn stress-strain properties (page 81)and that melting in the case of nylon and polyester fiber may limittheir ballistic effectiveness. Laible indicated that NOMEX, a heatresistant polyamide fiber with modest strength, possesses fairly goodballistic resistant properties (page 88).

Furthermore, in "The Application of High Modulus Fibers to BallisticProtection" R. C. Laible et al., J. Macromol. Sci.-Chem. A7(1), pp.295-322 1973, it is indicated on p. 298 that a fourth requirement isthat the textile material have a high degree of heat resistance; forexample, a polyamide material with a melting point of 255° C. appears topossess better impact properties ballistically than does a polyolefinfiber with equivalent tensile properties but a lower melting point. Inan NTIS publication, AD-A018 958 "New Materials in Construction forImproved Helmets", A. L. Alesi et al., a multilayer highly orientedpolypropylene film material (without matrix) referred to as "XP" wasevaluated against an aramid fiber (with a phenolic/polyvinyl butyralresin matrix). The aramid system was judged to have the most promisingcombination of superior performance and a minimum of problems for combathelmet development.

BRIEF DESCRIPTION OF THE INVENTION

It has been surprisingly found that extremely high tenacity polyethyleneand polypropylene materials of ultra high molecular weight performsurprisingly well as ballistic-resistant materials, in spite of theirrelatively low melting points. Accordingly, the present inventionincludes a ballistic-resistant article of manufacture comprising anetwork of polyolefin fibers having, in the case of polyethylene fibers,a weight average molecular weight of at least about 500,000, a tensilemodulus of at least about 300 grams/denier and a tenacity of at leastabout 15 grams/denier, and in the case of polypropylene fibers, a weightaverage molecular weight of at least about 750,000, a tensile modulus ofat least about 160 grams/denier and a tenacity of at least about 8grams/denier, said fibers being formed into a network of sufficientthickness to absorb the energy of a projectile. The invention includessuch articles in which the network is either a woven or knitted fabricor is a composite or a laminated structure.

DETAILED DESCRIPTION OF THE INVENTION

Ballistic articles of the present invention include a fiber network,which may be an ultra high molecular weight polyethylene fiber networkor an ultra high molecular weight polypropylene network.

In the case of polyethylene, suitable fibers are those of molecularweight of at least about 500,00, preferably at least about one millionand more preferably between about two million and about five million.The fibers may be grown in solution spinning processes such as describedin U.S. Pat. No. 4,137,394 to Meihuzen et al., or U.S. application Ser.No. 225,288 of Kavesh et al., filed Jan. 15, 1981, copending andcommonly assigned, or a fiber spun from a solution to form a gelstructure, as described in German Off. No. 3,004,699 and GB No. 2051667,and especially as described in application Ser. No. 259,266 of Kavesh etal. filed Apr. 30, 1981 and a continuation-in-part of Ser. No. 259,266,Ser. No. 359,020, filed herewith, both copending and commonly assigned.Examples of the gel spun fiber, and its use in preparing ballisticarticles, are given in the Examples below. Depending upon the formationtechnique, the draw ratio and temperatures, and other conditions, avariety of properties can be imparted to these fibers. The tenacity ofthe fibers should be at least about 15 grams/denier, preferably at leastabout 20 grams/denier, more preferably at least 25 grams/denier and mostpreferably at least about 30 grams/denier. Similarly, the tensilemodulus of the fibers is at least about 300 grams/denier, preferably atleast about 500 grams/denier and more preferably at least about 1,000grams/denier and most preferably at least about 1,500 grams/denier.These highest values for tensile modulus and tenacity are generallyobtainable only by employing solution grown or gel fiber processes. Manyof the fibers have melting points higher than the melting point of thepolymer from which they were formed. Thus for example, ultra highmolecular weight polyethylenes of 500,000, one million and two milliongenerally have melting points in the bulk of about 138° C. As describedfurther in Ser. No. 359,020, the highly oriented polyethylene fibersmade of these materials have melting points 7°-13° C. higher, asindicated by the melting point of the fiber used in Examples 5A and 5B.Thus, a slight increase in melting point correlates with the orientationimparted to the present fibers. Nevertheless, the melting points ofthese fibers remain substantially below nylon; and the efficacy of thesefibers for ballistic resistant articles is contrary to the variousteachings cited above which indicate temperature resistance as acritical factor in selecting ballistic materials.

Similarly, highly oriented polypropylene fibers of molecular weight atleast about 750,000, preferably at least about one million and morepreferably at least about two million may be used. Such ultra highmolecular weight polypropylene may be formed into reasonably welloriented fibers by the techniques prescribed in the various referencesreferred to above, and especially by the technique of U.S. Ser. No.259,266, filed Apr. 30, 1981, and the continuation-in-part thereof Ser.No. 359,020 filed herewith, both of Kavesh et al. and commonly assigned.Since polypropylene is a much less crystalline material thanpolyethylene, tenacity values suitable with polypropylene are generallysubstantially lower than the corresponding values for polyethylene.Accordingly, a suitable tensile strength is at least about 8grams/denier, with a preferred tenacity being at least about 11grams/denier. The tensile modulus for polypropylene is at least about160 grams/denier, preferably at least about 200 grams/denier. Themelting point of the polypropylene is generally raised several degreesby the orientation process, such that the polypropylene fiber preferablyhas a main melting point of at least about 168° C., more preferably atleast about 170° C.

In ballistic articles containing fibers alone, the fibers may be formedas a felt, knitted, basket woven, or formed into a fabric in any of avariety of conventional techniques. However, within these techniques, itis preferred to use those variations commonly employed in thepreparation of aramid fabrics for ballistic-resistant articles. Suchtechniques include those described in U.S. Pat. No. 4,181,768 and in M.R. Silyquist et al., J. Macromol. Sci.-Chem., A7(1) 203 et seq (1973).

In addition to the use of fabrics of fiber alone, it is contemplated touse fabrics of coated fibers. The present fibers may be coated with avariety of polymeric and non-polymeric materials, but are preferablycoated, if at all, with a polyethylene, polypropylene, or a copolymercontaining ethylene and/or propylene having at least about 10 volumepercent ethylene crystallinity or at least about 10 volume percentpropylene crystallinity. The determination of whether or not copolymershave this crystallinity can be readily determined by one skilled in theart either by routine experimentation or from the literature such asEncyclopedia of Polymer Science, vol. 6, page 355 (1967). Coated fibersmay be arranged in the same fashion as uncoated fibers into woven,non-woven or knitted fabrics. In addition, coated fabrics may bearranged in parallel arrays and/or incorporated into laminants orcomposites. Furthermore, the fibers used either alone or with coatingsmay be monofilaments or multifilaments wound or connected in aconventional fashion.

The proportion of coating in the coated fibers may vary from relativelysmall amounts (e.g. 1% by weight of fibers) or relatively large amounts(e.g. 150% by weight of fibers), depending upon whether the coatingmaterial has any ballistic-resistant properties of its own (which isgenerally not the case) and upon the rigidity, shape, heat resistance,wear resistance and other properties desired for the ballistic-resistantarticle. In general, ballistic-resistant articles of the presentinvention containing coated fibers generally have a relatively minor(e.g. 1-25%, by weight of fibers), since the ballistic-resistantproperties are almost entirely attributable to the fiber. Nevertheless,coated fibers with higher coating contents may be employed. More detailsconcerning coated fibers are contained in a copending application ofHarpell et al. Ser. No. 359,976, filed herewith and commonly assigned,the disclosure of which is hereby incorporated by reference to theextent not inconsistent herewith.

In addition to fibers and coated fibers, simple composite materials maybe used in preparing the ballistic-resistant articles of the presentinvention. By simple composite is intended to mean combinations of theultra high molecular weight fiber with a single major matrix material,whether or not there are other materials such as fillers, lubricants orthe like. Suitable matrix materials include polyethylene, polypropylene,ethylene copolymers, propylene copolymers and other olefin polymers arecopolymers, particularly those having ethylene or propylenecrystallinity. Suitable matrix materials also include, however, othermaterials which, in general, have a poor direct adherence to thepolyethylene or polypropylene fibers. Examples of such other matrixmaterials include unsaturated polyesters, epoxy resins and polyurethaneresins and other resins curable below the melting point of the fiber. Asin the case of coated fibers, the proportions of matrix to fiber is notcritical for the simple composites, with matrix amounts of about 5 toabout 150%, by weight of fibers, representing a broad general range.Also within this range, it is preferred to use composites having arelatively high fiber content, such as fibers having only about 10-50%matrix, by weight of fibers. One suitable technique of forming such highfiber composites is to coat the fibers with a matrix material and thento press together a plurality of such coated fibers until the coatingmaterials fuse into a matrix, which may be continuous or discontinuous.

The simple composite materials may be arranged in a variety of forms. Itis convenient to characterize the geometries of such composites by thegeometries of the fibers and then to indicate that the matrix materialmay occupy part or all of the void space left by the network of fibers.One such suitable arrangement is layers or laminates of fibers arrangedin parallel fashion within each layer, with successive layers rotatedwith respect to the previous layer. An example of such laminatestructures are composites with the second, third, fourth and fifthlayers rotated plus 45°, -45°, 90° and 0°, with respect to the firstlayer, but not necessarily in that order. Other examples includecomposites with alternating layers rotated 90° with respect to eachother. Furthermore, simple composites with short fiber lengthsessentially randomly arranged within the matrix may be used.

Also suitable are complex composites containing coated fibers in amatrix, with preferred complex composites having the above-describedcoated fibers in a thermoplastic, elastomers or thermoset matrix; withthermoset matrixes such as epoxies, unsaturated polyesters and urethanesbeing preferred.

EXAMPLES Preparation of Gel Fiber

A high molecular weight linear polyethylene (intrinsic viscosity of 18in decalin at 135° C.) was dissolved in paraffin oil at 220° C. toproduce a 6 wt. % solution. This solution was extruded through asixteen-hole die (hole diameter 1 mm) at the rate of 3.2 m/minute. Theoil was extracted from the fiber with trichlorotrifluoroethane(trademark Genetron® 113) and then the fiber was subsequently dried. Oneor more of the multifilament yarns were stretched simultaneously to thedesired stretch ratio in a 100 cm tube at 145° C. Details of samplestretching are given in Table 1, along with selected fiber properties.

In addition, Fiber E had a main melting peak at 144° C. by DSC at ascanning rate of 10° C./minute.

                  TABLE 1                                                         ______________________________________                                                       Stretch       Tenacity                                                                             Modulus                                                                              U.E.                               Fiber Example  Ratio   Denier                                                                              g/den  g/den  %                                  ______________________________________                                        A     1        12      1156  11.9   400    5.4                                .sup. B*                                                                            1,2      18      1125  9.4    400    4.0                                C     3,4      13      976   15.0   521    5.8                                D     5        17      673   21.8   877    4.0                                E     6        15      456   21.6   936    3.9                                F     7        18      136   27.6   1143   4.1                                ______________________________________                                         *Fiber B apparently retained some oil after extraction, thus accounting       for its inferior properties compared to Fiber F.                         

EXAMPLES 1-6

High density polyethylene film (PAXON®4100 high density polyethylene, anethylene-hexene-1 copolymer having a high load melt index of 10 made andsold by Allied Corporation) was placed on both sides of a three inch bythree inch (6.72 cm×6.75 cm) steel plate and then layers of parallelmultistrand yarn of high tenacity polyethylene yarn (as described below)were wound around the plate and film until the film on both sides wascovered with parallel fibers. Film was then again placed on both sidesand the yarn was wound in a direction perpendicular to the first layer.The process was repeated with alternating film and fiber layers, andwith adjacent fiber layers being perpendicular to each other until thesupply of fibers was exhausted or a fiber content of 7 g for each sidehas achieved. The wound plate was then molded under pressure for 30minutes at 130°-140° C. The sample was then removed and slit around theedges to produce an A and B sample of identical fiber type and arealdensity.

The above procedure was followed six times with the fibers indicated inTable 2. For Example 1, 37.4 weight % of the fibers used were asindicated by the line 1--1 and 62.6 weight % of the fibers were asindicated by the line 1-2.

                  TABLE 2                                                         ______________________________________                                               Fiber      Fiber                                                              Tenacity   Modulus         Fiber Wt %                                  Example                                                                              (g/denier) (g/denier)                                                                              UE*   Wt    Fiber                                 ______________________________________                                        1-1    16.3       671       4.6%  7.425 g                                                                             75.2                                  1-2    9.5        400       4.0%                                              2      9.5        400       4.0%  5.333 g                                                                             74.6                                  3      15.0       521       5.8%  7.456 g                                                                             75.5                                  4      15.0       521       5.8%  7.307 g                                                                             76.4                                  5      21.8       877       4.0%  7.182 g                                                                             74.7                                  6      21.6       936       3.9%  7.353 g                                                                             76.6                                  ______________________________________                                    

Bullet fragments of 22 caliber projectile (Type 2) meeting thespecifications of Military Specification MIL-P-46593A (ORD) were shot ateach of the composites at an approximate velocity of 347 m/sec using thegeometry of:

    ______________________________________                                        G        A        B        T      C      D                                    ______________________________________                                        5 feet   3 feet   3 feet   1.5 feet                                                                             3 feet                                      1.52 m   0.91 m   0.91 m   0.46 m 0.91 m                                      ______________________________________                                    

where G represents the end of the gun barrel; A, B, C and D representfour lumiline screens and T represents the center of the target plaque.Velocities before and after impact were computed from flight times A-Band C-D. In all cases, the point of penetration through screen Cindicated no deviation in flight path. The difference in these kineticenergies of the fragment before and after penetration of the compositewas then divided by the following areal densities of fibers to calculatean energy loss in J/(kg/m²):

    ______________________________________                                                    Fibral                                                            Example     Areal Density (kg/m.sup.2)                                        ______________________________________                                        1           1.28                                                              2           0.92                                                              3           1.28                                                              4           1.26                                                              5           1.24                                                              6           1.27                                                              ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                                                Kinetic                                               Tenacity     Velocity   Energy                                                (g/          (m/sec)    (J)        Loss                                       Ex.  Run    denier)  before/after                                                                           before                                                                              after                                                                              [J/(kg/m.sup.2)]                     ______________________________________                                        1    A      12.0     337.7/282.2                                                                            62.8  42.9 14.8                                 1    B      12.0     346.3/298.7                                                                            66.0  49.1 13.2                                 2    A      9.5      346.9/317.0                                                                            66.3  55.3 11.9                                 2    B      9.5      335.0/304.8                                                                            61.8  51.2 11.6                                 3    A      15.0     386.2/287.1                                                                            82.1  45.4*                                                                              28.7                                 3    B      15.0     335.0/277.4                                                                            61.8  42.4 15.2                                 4    A      15.0     333.1/274.9                                                                            61.1  41.6 15.5                                 4    B      15.0     335.3/277.7                                                                            61.9  42.5 15.4                                 5    A      21.8     353.0/287.1                                                                            68.6  45.4 18.7                                 5    B      21.8     343.2/277.1                                                                            64.9  42.3 18.2                                 6    A      21.6     343.8/247.8                                                                            65.1  33.8 24.6                                 6    B      21.6     337.4/249.0                                                                            62.7  34.2 22.5                                 ______________________________________                                         *Note the unusually high initial velocity for Example 3, Run A.          

Plotting the energy loss versus fiber tenacity shows a positivecorrelation, with the relationship being fairly linear, except for lowvalues for both composites of Example 5 (which may have experiencedfiber melting during molding).

EXAMPLE 7

The procedure of Examples 1-6 was repeated using a 26.5 g/denier fiber,except that only a single pair of composites was prepared. Then the twocomposites were molded together using a film of low density polyethylenebetween them. This composite had 68% fibers and a fiber areal density of1.31 kg/m². On firing, the velocities before and after impact were 1143ft/sec and 749 ft/sec (348.4 and 228.3 m/sec). The kinetic energiesbefore and after impact were 66.9 J and 28.7 J. The energy loss based on1.31 kg/m² fiber areal density was then 29.1 J/(kg/m²), which, whenplotted, falls on the line drawn through points from Examples 1-4 and 6.

COMPARATIVE EXAMPLE 8

Composites were prepared as in Examples 1-6 using a melt-spunpolyethylene fiber having a tenacity of 5.6 g/denier. Some fiber meltingoccurred during molding due to the close melting points of the melt spunfiber and the high density polyethylene fiber. On firing a projectilethe velocities measured before and after impact were 342.3 and 320.3m/sec (1123 ft/sec and 1051 ft/sec), for energies before and after of64.51 J and 56.5 J. The energy loss, based on a fibral areal density of1.31 kg/m² is 6.35 J/(kg/m²). substantially lower than the values forExamples 3-6 (being within the scope of the present invention), andlower even than values for Examples 1 and 2, where the fiber tenacitywas under 15 g/denier.

EXAMPLES 9 AND 10 AND COMPARATIVE EXAMPLE 11 EXAMPLE 9

A high tenacity polyethylene fiber (tenacity 18.4 g/denier, tensilemodulus 673 g/denier) was coated with low density polyethylene from atoluene solution. The polyethylene (tradename Union Carbide PE-DPA 6169NT) had a melt index of 6 and a density of 0.931 g/cm³. The coatedfibers were wound on a three inch by three inch (6.75 cm×6.75 cm) steelplate, with each layer wound perpendicular to the previous layer. Thewound plate was molded for 30 minutes at 120°-130° C. The composite wasthen cut around the edges and the two halves molded together with a thinfilm of low density polyethylene in the center to obtain a single plaquehaving 86.6 weight % fiber content. Ballistics testing of this plaque isdescribed below.

EXAMPLE 10

Example 9 was repeated using a high tenacity polyethylene fiber(tenacity 19.0 g/denier, modulus 732 g/denier) coated with high densitypolyethylene (tradename EA-55-100, melt index=10, density 0.955 g/cm³).After molding for 30 minutes at 130°-140° C., two composite plaques wereproduced (10A and 10B) each with 72.6 weight % fiber contact. Ballistictesting is described below.

COMPARATIVE EXAMPLE 11

For comparison, a 1500 denier KEVLAR® 29 aramid yarn (22 g/denier) wovenroving fabric prepregged with phenolic polyvinyl butyral resin (resincontent 20 weight %) was molded for 20 minutes at 166° C. Three suchplaques (11A, 11B and 11C) were prepared with a fiber areal density of1.04 kg/m² each.

BALLISTIC TESTING 11-13

The six composites of Examples 11 and 12 and of Comparative Example 13were taped over a 2.2 inch by 2.1 inch (5.6 cm×5.6 cm) cut in athree-eighths inch (1 cm) plywood sheet. Bullet fragments (0.22 type 2)according to Military Specification MIL-P-46593A (ORD) were firedthrough the plaques using the geometry of:

    ______________________________________                                        G        A        B        T      C      D                                    ______________________________________                                        5 feet   3 feet   3 feet   1.5 feet                                                                             3 feet                                      1.52 m   0.91 m   0.91 m   0.46 m 0.91 m                                      ______________________________________                                    

where G represents the end of the gun barrel; A, B, C and D representfour lumiline screens and T represents the center of the target plaque.Velocities before and after impact were computed from flight times A-Band C-D. In all cases, the point of penetration through screen Cindicated no deviation in flight path. The results are displayed inTable 4.

                  TABLE 4                                                         ______________________________________                                               Areal                                                                         Den-    Velocity              Energy                                   Com-   sity    (m/sec)     KE(J)     Loss                                     posite kg/m.sup.2                                                                            Before  After Before                                                                              After [J(kg/m.sup.2)]                      ______________________________________                                        9      1.11    327.7   226.2 59.1  28.2  27.9                                 10A    0.797   335.6   283.5 62.0  44.3  22.3                                 10B    0.797   331.3   278.3 60.5  42.7  22.3                                 11A    1.04    300.5   205.7 49.8  23.3  25.4                                 11B    1.04    342.6   273.4 64.7  41.2  22.6                                 11C    1.04    338.0   257.9 62.9  36.6  25.3                                 controls       336.2   324.9 62.3  58.2  --                                   (no com-       337.7   327.4 62.8  59.0  --                                   posites)                                                                      ______________________________________                                    

These results indicate comparable performance for composites preparedfrom polyethylene fibers of 18.4-19.0 g/denier tenacity and compositesprepared from aramid fibers of 22 g/denier. Since the process of Kaveshet al. can produce fibers of tenacity 30 g/denier, 40 g/denier orhigher, it is expected that these fibers would substantially outperformaramid fibers for ballistic applications.

EXAMPLES 12-13

Four 16 filament polyethylene xerogels were prepared according to theprocedure described above before Example 1, but with 16 spinnerettes.One of the yarns (having been prepared from a 22.6 IV polymer) wasstretched using one end at 140° C. (18:1); the other three yarns werestretched together (48 filaments) at 140° C. (17:1). The properties ofthese two yarns were measured and are displayed in Table 5 withpublished data on KEVLAR®-29 aramid yarn.

                  TABLE 5                                                         ______________________________________                                                 16 Fil    48 Fil  KEVLAR-29                                          ______________________________________                                        Denier     201         790     1043                                           Tenacity (g/den)                                                                         21          18      22                                             Modulus (g/den)                                                                          780         650     480                                            Elongation 3.9%        4.7%    3-4%                                           ______________________________________                                    

An aluminum plate; three inches×three inches×four-tenths inch (7.6cm×7.6 cm×1 cm) was wound with one yarn, then covered with a 1.4 mil(0.036 mm) thick high density polyethylene film (Allied Corporation's060-003), then wound in a perpendicular direction with yarn, then coatedwith film. After 10 fiber layers and 10 film were present on each sideof the plate, the covered plate was cured at 136.6° C. for 15 minutes at400 psi (2.76 MPa) pressure.

After molding, the composite ensemble was split around its edges toremove the aluminum plate. One of the 10 layer composites was retainedfor ballistic testing and the other was used as a central core forwinding an additional 6 yarn/film layers to prepare a compositecontaining a total of 22 yarn layers (both 16 fil yarn and 48 fil yarnwere used). The areal densities and the fiber areal densities of the 10layer and 22 layer ECPE composites are given in Table 2, below. Thefiber volume fraction was about 75% in each.

Ballistics testing of these composites are described below.

EXAMPLE 14

A fourteen layer composite similar to the twenty-two layer composite ofExample 13 was prepared by winding two fiber/film layers onto each sideof a similar ten layer composite. The fourteen layer composite had atotal areal density of 0.274 kg/m³ and fibral areal density of 0.167kg/m³. The same 16 and 48 fiber yarn was used.

COMPARATIVE EXAMPLE 15

Composites of Kevlar-29 aramid and polyester resin were prepared in asimilar manner except that the matrix polyester system was doctored ontoeach Kevlar layer to impregnate the ensemble. The polyester system wasVestopal-W plus 1% tertiary butyl perbenzoate and 0.5% cobaltnaphthenate. The ensembles were cured at 100°±5° C., for one hour atapproximately 400 PSI (2.76 MPa) pressure. The areal densities and fiberareal densities are given in Table II. The fiber volume fractions were75%.

BALLISTIC TESTING

Ballistic testing of the composites of examples 12-14 and theKevlar-29/polyester 3"×3" composite plaques of comparative Example 15were performed in a identical manner. The plaques were placed against abacking material consisting of a polyethylene covered water-filledurethane foam block. The density of the backing material was 0.93 g/cm³.The ammunition fired was 22 caliber, longrifle, high velocity, solidnose, lead bullets. The rounds were fired from a handgun of six inch (15cm) barrel length at a distance of six feet (1.8 m), impactingperpendicular to the plaque surface. Impact velocity was approximately1150 ft/sec (353 m/sec) (Ref: "Gunners Bible", Doubleday and Co., GardenCity, NY 1965).

The qualitative results are displayed in Table 6. In the column labeled"Penetration" the word "Yes" means that the bullet passed completelythrough the plaque; the work "No" means that the bullet was stoppedwithin the plaque.

                  TABLE 6                                                         ______________________________________                                                       Composite Areal                                                                            Fiber Areal                                                                             Pene-                                   Example                                                                              Layers  Density (g/cm.sup.3)                                                                       Density (g/cm.sup.3)                                                                    tration                                 ______________________________________                                        12     10      0.122        0.097     Yes                                     13     22      0.367        0.248     No                                      14     14      0.274        0.167     No                                      15A     7      0.131        0.097     Yes                                     15B    12      0.225        0.167     No                                      15C    18      0.360        0.256     No                                      ______________________________________                                    

These results indicate that the composites using polyethylene fibers of18-21 g/denier tenacity required roughly the same areal density(0.167±0.05 g/cm³) as the aramid composite to defeat the 22 caliberprojectile.

EXAMPLE 16 Mode of Failure

The fragment exit side of Example 7 was examined by scanning electronmicroscopy and found to have a fibrillar structure similar to thatreported for Kevlar® fibers (Ballistic Materials and PenetrationMechanics--R. C. Laible--Elsevier Scientific Publishing Company--1980).Fibers exhibited extensive longitudinal splitting similar to that foundwhen fibers were broken in an Instron Tensile Tester using a 10 inch(25.4 cm) length of fiber pulled at 10 in./min (25.4 cm/min). There wasno evidence of the smooth knobs shown at the end of impacted polyesterfibers shown in FIG. 6, Page 84--Ballistic Materials and PenetrationMechanics. (The knob-like structure at the end of the impacted polyesteris attributed to melting).

Example 2B (see Table 3) exhibited similar morphology after ballisticimpact, but the fibrillation was less extensive, and there was evidenceof a minor amount of melting.

We claim:
 1. A ballistic-resistant article of manufacture comprising anetwork of polyolefin fibers having, in the case of polyethylene fibers,a weight average molecular weight of at least about 500,000, a tensilemodulus of at least about 300 g/denier and a tenacity of at least about15 g/denier, and in the case of polypropylene fibers, a weight averagemolecular weight of at least about 750,000, a tensile modulus of atleast about 160 g/denier and a tenacity of at least about 8 g/denier,said fibers being formed into a network of sufficient thickness toabsorb the energy of a projectile.
 2. The ballistic-resistant article ofclaim 1 being in the form of a composite comprising said polyolefinfiber network and a matrix.
 3. The ballistic-resistant article of claim2 wherein said polyolefin fiber network comprises polyolefin fiberscoated with an ethylene or propylene copolymer and said matrix comprisesa thermoset resin, said copolymer having strong adhesion to saidpolyolefin fibers and to said thermoset resin matrix.
 4. Theballistic-resistant article of claim 2 wherein said matrix comprises athermoplastic having ethylene or propylene crystallinity.
 5. Theballistic-resistant article of claim 4 wherein said polyolefin fiber ispolyethylene and said thermoplastic matrix is polyethylene.
 6. Theballistic-resistant article of claim 5 wherein said polyethylene fiberhas a melting point of at least about 140° C. and said polyethylenepolymer matrix has a melting point at least about 3° C. lower than themelting point of said polyethylene fiber.
 7. The ballistic-resistantarticle of claim 5 wherein said polyethylene polymer matrix ispolyethylene of a density between about 0.90 and about 0.94 g/cm³. 8.The ballistic-resistant article or claim 5 wherein said polyethylenepolymer matrix is polyethylene of a density between about 0.94 and about0.98 g/cm³.
 9. The ballistic-resistant article of claim 2, 3, 4 or 5wherein said fiber network comprises a first plurality of layers, witheach layer comprising a second plurality of fibers.
 10. Theballistic-resistant article of claim 9 wherein said second plurality offibers are substantially aligned in each layer.
 11. The ballisticresistant article of claim 1 consisting essentially of a flexiblenetwork of said polyolefin fibers.